Accurately determining the position of moving objects, such as aircraft, missiles, land-vehicles, watercraft, and electronic devices (e.g., mobile telephones) has been a challenge for sometime. There have been many methods developed, including radar, sonar, GPS and other frequency based techniques.
Typically, object location systems make use of multilateration techniques (i.e., the fixing of a position by the time difference of arrival (TDOA) of a signal at a sensor) to locate the origin of a transmitted signal. TDOA information is typically based on signal arrival-time measurements from an object that transmits, reflects or receives and re-transmits a signal that is received at receiving sensors. The TDOA measurements and other sensor information is typically transmitted to a central processor for processing.
Methods for estimating position using TDOA are known. For example, “A Simple and Efficient Estimator for Hyperbolic Location” by Y. T. Chan and K. C. Ho. (IEEE Transactions on Signal processing, Vol. 42, No. 8, August 1994, pp. 1905–1915), which is incorporated herein by reference, provides techniques for implementing TDOA measurements.
Other methods for determining the location and identification of a object are also known. For example, U.S. Pat. No. 6,211,811, issued to Evers, discloses a method and apparatus for improving the surveillance coverage and object identification in a radar based surveillance system.
Another known method is disclosed in U.S. Pat. No. 6,201,499, issued to Hawkes et al. As disclosed therein, it is known to provide a method and apparatus for measuring the time difference of arrival between two received signals, each received signal being a time delayed version of a transmitted signal as intercepted at two different sensors where the transmitted signal is generated by a radio frequency transmitter.
Many drawbacks are present in existing systems and methods. For example, known systems and methods are often inaccurate and costly to implement. Other drawbacks also exist.